Extensible paper and the process of producing the same



Sept. 17, 1963 5. BACK ETAL EXTENSIBLE PAPER AND THE PROCESS OF PRODUCING THE SAME Filed June 29, 1959 DR YER? GU/DE POIZLS INVENTORS E 0 W m KL M w w rw HR A 65 a 5R United States Patent M 3,104,197 EXTENSIBLE PAPER AND THE PRGCES 6F PRQDUCKNG THE SAME Sangho Back and Robert E. Linde, (Jamas, Wash, assignors to Crown Zelierbach Corporation, San Francisco, Qalifi, a corporation of Nevada Filed June 29, 1959, Ser. No. 823,544 13 Qlaims. (til. 162-113) This invention relates to extensible papers and particularly to an improved extensible paper and a method and apparatus for making a superior paper of this kind having greater extensibility, flexibility and strength than comparable papers made by known methods.

Extensible papers used in the manufacture of bags and wrappiugs as well as for other purposes have been manuf actured by various processes. Some such processes depend upon creping the paper during its manufacture by any one of several known methods. The resulting product has considerable stretch or extensibility in one direction but its creped surface renders it undesirable for some purposes and particularly for the manufacture of bags or the like upon which advertising or other information is printed because the irregularities of the creped surface make printing difficult. Such papers are also of relatively low strength. One process for the manufacture of extensible paper eliminates the undesirable creped effect of the surface of the paper [and produces a paper which is readily adaptable to printing. However this process is complex and costly and involves the use of extensive machinery which utilizes a great deal of space. It also employs high temperature and high pressure and requires extensive modifications of the paper making machine with which it is used.

The latter process and most, if not all, creping processes rely upon a sort of compressing or gathering of the paper web during or after its manufacture and this takes place by a retarding or rearranging of the paper or the pulp fibers in it as it advances through a machine. This produces an eiiect on the paper in what is termed the cross mac-hine direction so that the paper is made extensible lengthwise of the web or in the with-machine direction with little or no beneficial result in the crossmachine direction of the finished product. This is true for example of ordinary blade icreped papers such as toweling or tissues characterized by low strength.

Other methods of crepin-g have been described wherein the elastic property of rubber or like material is emplayed for imparting a creped effect in one or both directions of the paper. These methods, however, employ an elastic band or blanket in conjunction with a hard surface and include the compression of the paper against the hard surface over a considerable area during the creping.

It is an object of the present invention to provide a creped paper and process of producing the same which paper is extensible in both with-machine and cross-machine directions which has one smooth easily printable side, which possesses toughness in excess of those normally found in extensible papers either of the fiat or conventionally oreped type and which possesses extensibility well in excess of that possessed by known types of papers.

It is also a related object of the present invention to provide an extensible paper and process of forming the same by simultaneously creping and embossing the paper to give it extensibility in all directions.

Another object of the invention is to provide a paper and process which can be made by apparatus low in original cost, simple and inexpensive to operate and capable of producing a uniformly compressed creping in a paper web and optionally simultaneously embossing the web to produce any one of numerous patterns therein and to create cross-machine extensibility of the web.

Patented Sept. 17, 1963 A still further object of the invention is to provide a process which may be carried out by an apparatus of the kind referred to which is readily adaptable to use with conventional paper making machines and can be combined therewith with .a minimum use of space and a minimum of alterations to the conventional machine.

Still further objects and advantages of the invention reside in the construction and arrangement of its several components and in the manner in which it is carried into practice and these will become apparent upon an understanding of the following description wherein reference is made to the accompanying drawings.

In the drawings:

FIG. 1 is a schematic view illustrating the location of apparatus for performing the present invention in the drying section area of a paper machine;

FIG. 2 is a diagrammatic sectional view of the principal elements of the apparatus of the present invention;

and

FIG. 3 is a fragmentary elevation of a part of the hard roll shown in FIG. 2 showing a modification.

The apparatus consists, as illustrated in FIG. 1, of a hard roll in and a soft or rubber covered roll 11 rotatable as on shafts 12 and 13, respectively, and arranged to form a nip between which a web of paper schematically illustrated at 14 may pass. With the web of paper coming from a paper making machine in a partially dried state, the arrangement of rolls shown produces a creping of the paper because the rubber surface in contact with the paper is distorted or stretched as it advances toward the center of the nip and as it passes the center it contracts -to its original length moving back toward the center of the nip or against the direction of travel of the paper thus distorting the paper and producing a crepe elfect.

As illustrated in FIG. 1 the rolls 10 and 11 are convemently positioned in the drying section of a paper machine between sets of dryer rolls and suitable guide rolls. The location is at a point in the drying section where the web 14 has been only partially dried as hereina'fter explained.

The use of rubber or rubberous material in conjunction with a hard surface in the manner described is known in the treatment of paper as well as fabrics but only in a general way and the present invention includes the use of rubber considerably softer and more elastic than previously used. Also of guest importance in the pro duction of an extensible paper by creping it in this manner is the idiifepential in speeds at which the rolls are destroying the creping effect. If the hard sunface carries an embossed pattern, a simultaneous crepe-embossing takes place.

In practicing the invention, normally refined pulp is formed in the usual manner on the wet end of a paper machine of conventional type, such for example as a Fourdrinier or a cylinder Wire machine. Water is removed from the web in the usual manner and the web is dried to a moisture content ranging from 20% to 60%, preferably 30% to 40% based on the oven-dry weight of the paper web depending upon the type of pulp being used. For example for soft pulp such as used in the manufacture of tissue and toweling, it would be some- 3 what less than 35% Whereas for a hard pulp it might be as high as 40%.

The softness of the rubber on the roll 11 is critical and contributes materially to the successful mmufacture of the paper of the present invention. The softness of the natural or synthetic rubber, as synthetics such as Buna N and porous-type neoprene can be successfully used, is measured by the Shore .durometer hardness test and should be within a range of from to 45 Shore durometer, the optimum being from 30 to 40. With rubber having this degree of softness, less pressure is required to deform or stretch the rubber a given amount, however softness also tends to create a coarser crepe. The sunface grind of the rubber also affects the crepe characteristics, a fine grind yielding a fine crepe pattern. However, a very smooth or emery cloth type of finish on the rubber is undesirable. While a natural rubber has been [found to perform somewhat better than synthetic rubbers, the latter resist heat md oxidation better than natural rubber and, therefore, economically may be preferred. One of the principal reasons for the softness Olf the rubber is that its recovery from the distortion, which is greatest at the center of the nip, is rapid and produces better, more uniform creping than that which occurs with harder rubber and renders the paper more extensible and more durable.

An optional embodiment of this invention includes the provision of means to improve the adherence of the paper web to the surface of the rubber roll as it passes through the nip. This may be accomplished by providing multiple perforations in the rubber as indicated at in FIG. 2 and a stationary suction box 18 mounted within the roll opposite the nip. Suction means, not shown, communicating with the box as through a line 1? will enhance adherence of the web to the rubber roll.

It is essential in practicing the present invention that the hard roll be operated at a surface speed greater than the soft rubber covered roll and that it has less afirnity for the surface of the paper than the soft roll so that the rubber covering on the soft roll will be extended or distorted in the manner illustrated in FIG. 2 of the drawing. Through this greater speed of the hard roll, the crimping effect is enhanced and a calendcring effect takes place on the surface of the paper in contact with the hard roll resulting in a relatively smooth surface finish which can be readily printed upon though the paper is in fact creped. The relative speeds of the rolls may be varied considerably but the benefits obtained through differential speeds are obtained only when the difference is 8% or greater. The degree of creping increases with the percentage of speed diiferential between the two rolls. The pressure between the rolls at the nip may be relatively light and pressures as low as 10 pounds per linear inch have produced a satisfactory product.

Various materials may be used for the surface of the hard roll such as Microrok, granite or other stones finished to a smooth but not highly polished surface. The most desirable effects have been obtained with a Microrok covered roll. Steel rolls have also been used successfully.

One feature of the invention, and that which greatly increases extensibility of the paper in the cross-machine direction is the embossing of the paper simultaneously with the creping operation. This embossing may be accomplished by ribs such as shown at 3.6 in FIG. 3 projecting from the surface of the roll to form indentations in the paper as it is creped and, due to the use of the soft rubber which recovers quickly after passing the center of the nip, a quick sharp pressure is applied to the moist paper forcing it against the ribs 16 and against the sunface of the roll between the ribs to create an embossed effect. Care is taken to maintain the pressure below a value which would destroy the creped surface between the ribs. The size and spacing of the ribs may be varied and many patterns other than the straight ribbing illustrated may be employed to obtain a like effect. This simultaneous creping and embossing of the product adds greatly to the cross-machine extensibility of the paper.

Papers having a stretch as high as 26% in the withmachine direction and 7% in cross-machine direction have been produced by the method and apparatus of the present invention. in addition, these papers show a marked increase in toughness as measured by the rupture energy test. It has also been determined that the simultaneous creping and embossing produces a different appearance and a distinctly better effect than is obtained by creping and embossing in two separate steps. The rigidity of the paper is reduced markedly and papers such as used for toweling or the like are softer and more uniformly creped by the present process than they are with other known processes. Furthermore the loss in tensile strength due to creping by the process of the present invention is insignificant as compared to that occurring in the manufacture of blade creped papers. The crcped or creped and embossed paper from the nip in which it is processed is directed into a drying apparatus, such as the remaining drying section of a conventional paper machine as shown in FIG. 1 with low tension to minimize pulling out the crepe and it is dried to the desired final moisture content.

The size of the apparatus described is such that it may be easily disposed within the drying section of a conventional paper making machine and, since its incorporation in such a machine and the means to drive the rolls at a speed related to the normal operating speed of the machine, is a matter readily understood by those skilled in the art and not pertinent to an understanding of the invention, these mechanical features are not herein disclosed.

One important feature of the present invention which contributes to the manufacture of the improved product described is the fact that the creping of the paper is effected quickly, under low pressure and particularly in an extremely short zone of treatment. That is to say, the entire creping process is accomplished at the recovery or recoil zone of the rubber roll. This zone is not substantially greater and may even be less than one-half inch in the direction of the travel of the paper web. As an example, rolls having a 22 inch diameter will produce actual creping in a distance of about 0.3 inch. This distinguishes the present invention from known processes in which the creping of paper includes compressing it between a rubber belt and a hard surface over a considerably greater distance.

Furthermore, the present process may be carried out without heat during the creping so that the hard roll may be operated at normal temperature which extends the life of the rubber roll against which it acts.

We claim:

1. A process for making a creped, extensible paper having a substantial amount of stretch and a toughness in excess of that of conventionally creped paper produced from the same pulp which comprises passing a paper web having a moisture content between about and about 60% through a nip formed by a hard roll and an elastic roll having a Shore duromcter hardness of from 10 to 45, said hard roll being driven at a surface speed greater than the speed of said elastic roll, compressively creping said Web in said nip while simultaneously smoothing one side thereof contacting the surface of said hard roll without disturbing the creped texture on the other side, and drying the paper web after passage through said nip.

2. The process of claim 1 wherein the moisture content of the web is between about 30% and about 3. The process of claim 1 wherein the hard roll is driven at a surface speed at least 8% greater than the speed of the elastic roll.

4. The process of claim 1 wherein the elastic roll has a Shore durorneter hardness of from 30 to 40.

5. The process of claim 1 wherein the Web is creped in an area of less than one-half inch in the direction of travel of said web.

6. The creped paper product produced by the process of claim 1.

7. A process for making a creped, extensible and embossed paper having a substantial amount of stretch and a toughness in excess of that of conventionally creped paper produced from the same pulp which comprises passing a paper web having a moisture content between about 20% and about 60% through a nip formed by a hard roll and an elastic roll having a Shore durorneter hardness of from to 45, said hard roll being driven at a surface speed greater than the speed of said elastic roll, compressively creping said web in said nip while simultaneously impressing an embossed design on said web during its passage through said nip to increase the extensibility of said web in the cross-machine direction and smoothing one side of said web contacting the surface of said hard roll without disturbing the creped texture on the other side, and drying said web after passage through said nip.

8. The process of claim 7 wherein the moisture content of the web is between about 30% and about 40%.

9. The process of claim 7 wherein the hard roll is driven at a surface speed at least 8% greater than the speed of the elastic roll.

10. The process of claim 7 wherein the elastic roll has a Shore durorneter hardness of from 30 to 40.

11. The creped paper product produced by the process of claim 7.

12. The process of claim 7 wherein spaced, parallel, longitudinal indentations are impressed in the web simultaneusly with the creping thereof without destroying the creped surface of the Webbetween the indentations.

13. The creped paper product produced by the process of claim 12.

References Cited in the file of this patent UNITED STATES PATENTS 1,548,790 Lorenz Aug. 4, 1925 1,911,001 Sheesley May 23, 1933 1,946,838 Cofrin Feb. 13, 1934 1,954,284 Davies Apr. 10, 1934 2,021,975 Wrigley et al. Nov. 26, 1935 2,043,351 Fourners et al. June 9, 1936 2,146,694 Wrigley et al. Feb. 7, 1939 2,535,734 Grettve Dec. 26, 1950 2,623,572 Haas Dec. 30, 1952 2,624,245 Cluett Jan. 6, 1953 2,825,117 Evans et al. Mar. 4, 1958 2,874,618 Yang Feb. 24, 1959 2,947,058 Landells et al. Aug. 2, 196-0 FOREIGN PATENTS 25,539 Great Britain 1907 26,068 Great Britain 1907 

7. A PROCESS FOR MAKING A CREPED, EXTENSIBLE AND EMBOSSED PAPER HAVING A SUBSTANTIAL AMOUNT OF STRETCH AND A TOUGHNESS IN EXCESS OF THAT OF CONVENTIONALLY CREPED PAPER PRODUCED FROM THE SAME PULP WHICH COMPRISES PASSING A PAPER WEB HAVING A MOISTURE CONTENT BETWEEN ABOUT 20% AND ABOUT 60% THROUGH A NIP FORMED BY A HARD ROLL AND AN ELASTIC ROLL HAVING A SHORE DUROMETER HARDNESS OF FROM 10* TO 45*, SAID HARD ROLL BEING DRIVEN AT A SURFACE SPACED GREATER THAN THE SPEED OF SAID ELASTIC RIOLL, COMPRESSIVELY CREPING SAID WEB IN SAID NIP WHILE SIMULTANEOUSLY IMPRESSING AN EMBOSSED DESIGN ON SAID WEB DURING ITS PASSAGE THROUGH SAID NIP TO INCREASE THE EXTENSIBILITY OF SAID WEB IN THE CROSS-MACHINE DIRECTION AND SMOOTHING ONE SIDE OF SAID WEB CONTACTING THE SURFACE OF SAID HARD RILL WITHOUT DISTRIBUTING THE CREPED TEXTURE ON THE OTHER SIDE, AND DRYING SAID WEB AFTRER PASSAGE THROUGH SAID NIP. 